Magnetic bubble memories are well known in the art. The most familiar type of bubble memory is referred to as the "field-access" type because a uniform magnetic field reorienting in the plane of bubble movement causes the bubbles to pass a detector sequentially. Such a field-access memory is characterized by a pattern of magnetically soft elements which defines paths for bubble movement in response to the reorienting in-plane field, as is well known.
The magnetically soft elements also typically define an expansion detector arrangement to which magnetic bubbles are moved. The detector arrangement includes consecutive columns of chevron elements, succeeding ones of which typically include greater numbers of elements. The detector stage is defined by the column with the greatest number of elements. The elements of the detector stage are interconnected to define a magnetoresistive element responsive to the presence of an elongated bubble to generate an output signal. Detection elements of this type are described in A. H. Bobeck U.S. Pat. No. 3,810,132, issued May 7, 1974.